The present invention relates to a tapered roller bearing which is used in differentials for motor vehicles and industrial machines, a tapered roller bearing apparatus which utilizes the tapered roller bearing and an automotive pinion shaft supporting apparatus which utilizes the tapered roller bearing apparatus.
Since tapered roller bearings are characterized in that they have a high load capacity and a high rigidity, compared to ball bearings, the tapered roller bearings are used in automotive pinion shaft supporting apparatuses in differentials and transaxles of motor vehicles. However, since the tapered roller bearings also have a drawback of a large running torque (loss), techniques in which raceways of inner and outer rings and rolling contact surfaces of tapered rollers are crowned to reduce the rolling friction (refer to, for example, Patent Document Nos. 1 to 2) have been proposed.
In the tapered roller bearings described Patent Document Nos. 1 to 2, the performance gain of the tapered roller bearings was attempted to be realized by controlling the shapes of crownings applied to the raceway surfaces and the rolling contact surfaces. However, no attempt had been made to control the amounts of crownings so as to reduce the running torque of a tapered roller bearing by paying attention to an idea in which crowning is taken as quantity. On the other hand, while one of main causes of the generation of running torque in a tapered roller bearing in a differential is the rolling viscous resistance of tapered rollers and the agitation loss of oil, there had been provided no clear guideline on how to reduce them.
To cope with this, the present applicant proposed a tapered roller bearing which could reduce the running torque effectively in consideration of various factors (Patent document No. 3).
The tapered roller bearing so proposed includes an outer ring, an inner ring, a plurality of tapered rollers interposed between the outer and inner rings and a cage for the tapered rollers,
wherein where z represents the number of tapered rollers, LWR represents a roller effective length, DW represents a roller mean diameter and dm represents a roller PCD, a roller filling rate which is expressed by z·DW/(π·dm) is in the range of 0.7 to 0.92, and a ratio of a roller length to a roller diameter which is expressed by LWR/DW is in the range of 1.1 to 1.7, and
wherein where RCO represents a crowning radius of the outer ring, LRO represents a raceway length of the outer ring, RCI represents a crowning radius of the inner ring and LRI represents a raceway length of the inner ring, an outer ring crowning parameter (=RCO/LRO) is 30 to 150, and an inner ring crowning parameter (=RCI/LRI) is 50 to 260. Thus, since the oil agitation loss and the rolling viscous resistance are reduced by reducing the roller length/roller diameter while maintaining the roller filling rate within the narrow range and the rolling viscous resistance is reduced by setting the crowning parameters in those ways, the running torque can be reduced effectively.
In addition, the proposed roller bearing includes an outer ring, an inner ring, a plurality of tapered rollers interposed between the outer and inner rings and a cage for the tapered rollers,
wherein where z represents the number of tapered rollers, LWR represents a roller effective length, DW represents a roller mean diameter and dm represents a roller PCD, a roller filling rate which is expressed by z·DW/(π·dm) is in the range of 0.7 to 0.92, and a ratio of a roller length to a roller diameter which is expressed by LWR/DW is in the range of 1.1 to 1.7, and
wherein respective raceway surfaces of the outer ring and the inner ring and rolling contact surfaces of the tapered rollers are crowned such that:
a total crowning amount (depth) (=outer ring crowning amount+inner ring crowning amount+roller crowning amount×2) is 50 μm or larger;
an outer ring crowning rate (=outer ring crowning amount/total crowning amount) is 40% or larger; and
a roller crowning rate (=(roller crowning amount×2)/total crowning amount) is 20% or smaller. Thus, the oil agitation loss and the rolling viscous resistance are reduced by reducing the roller length/roller diameter while maintaining the roller filling rate within the narrow range and the rolling viscous resistance is reduced by setting the crowning amounts in those ways.    Patent Document No. 1: JP-A-2003-130059    Patent Document No. 2: JP-A-2001-65574    Patent Document No. 3: WO2005100809 (PCT/JP2005/7260)
While the tapered roller bearing proposed by the present applicant can reduce the running torque largely by controlling the amounts of crownings and the shape of tapered rollers, compared to the conventional tapered roller bearings that had been proposed before then, when the contact angle is increased in order to reduce the oil agitation loss, the LWR/DW approaches from 1.7 to 1.1, and the diameter of the roller is increased. On the other hand, when the diameter of the roller increases, in order to increase the strength of the rib surface of the large rib portion against which large diameter side end faces of the rollers slide, the contact position (refer to e in FIGS. 1 to 2) between the rib surface and the larger diameter side end faces is raised, and as a result, there may occur a case where the running torque is increased in a low rotational speed range of 10 to 300 rpm.